This invention relates to a coaxial starter motor and more particularly to a coaxial starter motor with a planetary speed reduction gear.
In FIG. 1 in which the conventional engine starter motor is illustrated in a longitudinal sectional view, reference numeral 1 designates an armature of a d.c. motor, and an armature coil 3 is wound on an armature iron core 2 and connected to a commutator 4. The armature comprises a rotary shaft 5 on which the armature iron core 2 and the commutator 4 are secured. Magnetic poles 6 made of permanent magnets are secured to a yoke 7. A rear bracket 8 and a front bracket 9 are mounted to the yoke 7. A brush holder 10 supporting electric brush is mounted to the rear bracket 8 by bolts 11. The rear end of the rotary shaft 5 is supported by a bearing 12 attached to the rear bracket 9.
The starter motor comprises a planetary gear speed reduction unit 13 composed of a spur gear 14 which is a sun gear formed on the front side circumference of the rotary shaft 5, a stationary frame 15 fixed to the front bracket 10 and has an inner gear 16 formed on the inner circumference of its large-diameter portion, and planetary gears which are in mesh with the spur gear 14 and the inner gear 16 and which are rotatably supported by a support pin 18 and a bearing 19 mounted on the flange portion 21 formed at the rear end portion of the output shaft 20 to rotate around the spur gear 14 while it is spinning.
The output shaft 20 has formed helical splines 22 on its outer circumference and its front end is supported by the front bracket 9 through a bearing 23 while its rear end supports the rotary shaft 5 through a bearing 24. Between a central bore of the front end of the rotary shaft 5 and a recess in the rear end of the rotary shaft 5, a steel ball 25 is disposed to support thrust load in two directions. The rear portion of the output shaft 20 is supported by a bearing 26 supoorted by the stationary frame 15, a stopper 27 is rotatably but axially immovably fitted around the output shaft 20 by a stop ring 28.
The starter motor also comprises an over-running clutch 29 for transmitting the rotation of the output shaft 20. The over-running clutch 29 comprises a clutch outer member 30 which has helical splines 31 formed in its inner circumference and which axially movably engages the helical splines 22 and a clutch inner member 32 to which the rotation is unidirectionally transmitted through rollers 34. The clutch inner member 32 has a pinion 33 on its outer end. A stop ring 35 mounted to the clutch outer member 30 and a bearing 36 for supporting the clutch inner member 32 relatively rotatably and axially movably with respect to the output shaft 20.
The starter motor also comprises a solenoid switch 37 which comprises a case 38 which is mounted to the front bracket 9 and serves as a yoke. With in the case 38, an excitation coil 39 wound on a bobbin 40 made of synthetic resin is disposed, and a stationary iron core 41 is fixed at the rear end of the case 38. A movable iron piece or a plunger 42 is biased by a return spring 43 to the forward position. The plunger 42 supports a movable rod 44 for movement therewith. Also provided are an insulating cap 45 mounted on the outer end of the case 38, a support rod 46 axially movably supported in the stationary iron piece 41 and biased toward the forward position by a compression spring 47, a movable contact 48 mounted on the support rod 46 by an insulating member 49 and biased by a compression spring 50, and a stationary contact 51 mounted on the insulating cap 45 by a nut 52 so as to correspond to the movable contact 48.
Further, the starter motor comprises an electrical conductor 53 connected between the stationary contact 51 and the brush holder 10, a shift lever 54 supported at its center by the front bracket 9 and rotatably connected at its upper end to the movable rod 44. The shift lever 54 has a folked end which engages the engagement ring 35 of the over-running clutch 29. The rotation of the shift lever 54 causes the forward or backward movement of the engagement ring 35.
When it is desired to start the engine, an ignition switch (not shown) is turned on to energize the excitation coil 39 thereby to magnetically attract the plunger 42 to the stationary iron core 41. This causes the movable contact 48 to be brought into contact with the stationary contact 51 to rotate the armature 1. The rotation of the armature 1 is transmitted from the rotary shaft 5 to the planetary gear speed reduction unit 13 and then the speed-reduced rotation is tranmitted to the over-running clutch 29.
On the other hand, the rearward movement of the plunger 42 causes the shift lever 54 to be rotated counterclockwise to move forward the over-running clutch 29, whereby the pinion 33 is brought into mesh with a ring gear (not shown) of the engine flywheel to start the engine.
With the conventional starter motor of the arrangement as above described, the solenoid switch 37 is mounted above the yoke 7 of the motor, enevitably increasing the height of the starter motor, disadvantageously requiring a relatively large space for installation. Also, an output shaft 20 which is in series with the rotary shaft 5 is neccessary, so that the structure is complicated, and numbers of the parts must be precision machined for an accurate coaxial assembly of the two shafts. Further, since the shift lever 54 is neccessary to move the over-running clutch 29 forward or backward, which increases the number of the parts and the space for installing it.
Since the front bracket 9 is disposed close to the pinion 33, the an installation limitation is imposed upon the connection between the pinion 33 and the ring gear of the engine. Also, the inner sleeve 32 is disposed around the outer circumference of the output shaft 20, so that changing of the outer diameter or the number of the teeth of the pinion 33 is severly limited.